The increased use of mobile devices provides an untapped resource for delivering library resources to patrons. The mobile catalog is the next step for libraries in providing universal access to resources and information. This talk will share Oregon State University (OSU) Libraries' experience creating a custom mobile catalog. The discussion will first make the case for mobile catalogs, discuss the context of mobile search, and give an overview of vendor and custom mobile catalogs. The second half of the talk will look under the hood of OSU Libraries' custom mobile catalog to provide implementation strategies and discuss tools, techniques, requirements, and guidelines for creating an optimal mobile catalog experience that offers services that support time critical and location sensitive activities.